In the development for higher integration and higher performance of a semiconductor integrated circuit (referred hereinafter to as LSI), new fine processing techniques have been developed. Chemical mechanical polishing (hereinafter, referred to as CMP) that is one of such fine processing techniques is a technique used frequently in a process for manufacturing LSI, particularly for flattening of an interlayer insulation film, formation of a metal plug and formation of an embedded metal wiring in a process for forming a multilayer wiring, and is described in, for example, U.S. Pat. No. 4,944,836.
For higher performance of LSI, it is recently attempted to use a copper alloy as a wiring material. However, the copper alloy is hardly finely processable by dry-etching used frequently in forming a conventional aluminum alloy wiring. Accordingly, a damascene process is mainly used in which a copper-alloy thin film is deposited and embedded on an insulating film having a groove previously formed thereon and then the copper-alloy thin film on a part other than the groove is removed by CMP, thereby forming an embedded wiring, and this damascene process is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-278822.
CMP for metal generally involves attaching a polishing pad onto a circular polishing platen, impregnating the surface of the polishing pad with a metal polishing liquid, pressing against the pad the side of a substrate on which a metallic film was formed, and rotating the polishing platen while applying a predetermined pressure (hereinafter referred to as polishing pressure) from the backside of the substrate so as to remove a convex portion of the metallic film by the mechanical friction between the polishing liquid and the convex portion of the metallic film.
A metal polishing liquid used in CMP comprises generally of an oxidizer and abrasive particles and contains if necessary a metal oxide solubilizer, a metal anticorrosive etc. In an estimated basic mechanism, the surface of a metallic film is first oxidized by the oxidizer, and then the resultant oxidized film is removed by the abrasive particles. The oxidized layer in a concave part of the metallic film is less likely to contact with the polishing pad and does thus not undergo abrasion with abrasive particles, while a convex part of the metallic layer is removed with the progress of CMP, to flatten the surface of the substrate (see, for example, Journal of Electrochemical Society, Vol. 138, No. 11, pp. 3460 to 3464 (1991)).
However, when a wiring is formed by embedding with CMP using a conventional metal polishing liquid containing abrasive particles, the following problems arise: (a) generation of scratches attributable to solid particles, (b) deteriorations in flatness such as a phenomenon in which only the central portion of the surface of an embedded metallic wiring is isotropically polished to form a dish-like recess (referred to hereinafter as dishing) and a phenomenon in which an interlaminar insulation film together with the wiring metal is polished to form a recess (referred to hereinafter as erosion), (c) complexity in a washing process for removing abrasive particles remaining on the surface of a substrate after polishing, and (d) higher costs attributable to the cost of a solid abrasive itself and to waste liquid treatment.
For solving deteriorations in flatness by suppressing the generation of dishing, erosion and scratches to form highly reliable LSI wirings, a method of using a metal polishing liquid comprising a metal oxide solubilizer consisting of aminoacetic acid such as glycine or amidosulfuric acid and a protective film-forming agent such as BTA (benzotriazole) has been proposed (see, for example, Japanese Patent Application laid-Open No. 8-83780). The method of solving deteriorations in flatness by the protective film-forming effect of BTA etc. can prevent generation of dishing and erosion, but the polishing rate may be undesirably significantly reduced.
On the other hand, abrasive particles adhering by CMP to a substrate are removed mainly by physical washing with a brush made of polyvinyl alcohol or by sonication. As abrasive particles adhering to a substrate are made finer, however, it becomes more difficult to exert physical strength effectively on the abrasive particles.
As a polishing liquid for a metallic film, particularly for copper or a copper-based metal, a polishing liquid substantially free of abrasive particles is disclosed in, for example, Japanese Patent No. 3371775. According to this patent, a polishing liquid comprising an oxidizer for oxidizing a metallic film to be polished, an organic acid for water-solubilizing an oxide formed by oxidization with the oxidizer, water and if necessary an anticorrosive (protective film-forming agent) is used to exert mechanical friction on the surface of a metal, whereby an embedded metal wiring can be formed. For example, a method of forming a copper wiring with a polishing liquid containing hydrogen peroxide, citric acid and benzotriazole and substantially free of abrasive particles is described therein as one example, to solve the problems (a) to (d) described above. However, this method has a problem that the polishing rate under usual polishing conditions is 80 to 150 nm/min., and even if a high polishing loading of 300 g/cm2 or more is applied, the polishing rate is saturated and will not exceed 200 nm/min. To cope with this problem, a method of forming an embedded metal wiring by exerting mechanical friction on a metallic surface with a metal polishing liquid containing an oxidizing substance, phosphoric acid, an organic acid, a protective film-forming agent and water and substantially free of abrasive particles has been proposed (see Japanese Patent Application laid-Open No. 2002-50595). It is described that this method can solve the above-mentioned problems (a) to (d), can realize a higher polishing rate (700 nm/min. or more) and can process an object so as to have a shape reducing dishing and erosion to about 50 nm or less. Because this metal polishing liquid is substantially free of a polishing abrasive, erosion scarcely occurs.
On the other hand, there is no description therein of wiring width and wiring density, and according to our experiments, the dishing of a Cu wiring in a part of Cu wiring width/wiring space=100 μm/100 μm on a SEMATECH 854 pattern mask wafer polished with this polishing liquid is 100 nm or more, thus making it unusable as a metal polishing liquid for forming an embedded Cu wiring at the level in and after technology node 130 nm (hp 130). As used herein, the technology node refers to a generation of semiconductor technology and is expressed as half (half pitch) of the minimum wiring pitch of DRAM word line/bit line (see, for example, ITRS (International Technology Roadmap for Semiconductors) for 2003 published by US SEMATECH (Semiconductor Manufacturing Technology Institute).
As described above, the metal polishing liquid to which a polishing abrasive is not added or an ultratrace amount of a polishing abrasive is added can solve scratches and erosion, the necessity for removal of a polishing abrasive after polishing, a problem such as higher costs attributable to the cost of a solid abrasive itself and to waste liquid treatment and a problem in polishing rate aimed at improving throughput, but has hardly reduced dishing contributing significantly to the reliability and performance of a wiring. The conventional polishing liquid has a problem that it causes significant dishing mainly on a wide-width wiring part and cannot be used as a metal polishing liquid for forming an embedded Cu wiring at the level in and after the technology node 130 nm.
The present invention provides a metal polishing liquid capable of CMP at a high Cu polishing rate and solving the problems: (a) generation of scratches attributable to solid particles, (b) generation of deteriorations in flatness such as dishing and erosion, (c) complexity in a washing process for removing abrasive particles remaining on the surface of a substrate after polishing, and (d) higher costs attributable to the cost of a solid abrasive itself and to waste liquid treatment, that is, a metal polishing liquid capable of forming an embedded Cu wiring at the level in and after the technology node 130 nm as well as a method of polishing a film to be polished by using the same.